People often carry important items with them, such as passports, plane tickets, watches, medicine, eyeglass cases, security cards, laptop computers, car keys, AC adapter plugs, cameras, cell phones, or even gold pens. When traveling, either long distances or simply to a business meeting, people often pack and unpack these items, or carry the items in more than one bag. These items are therefore sometimes left behind when leaving taxis, packing for vacation, checking out of a hotel, or leaving a business meeting. Even if not left behind, a person must worry about ensuring that all important items are with him or her.
Several systems exist for using radio frequency identification (RFID) for tracking or identifying objects. RFID kits can be purchased, and RFID tags placed on items. The RFID tag can then be identified using a scanner. This presents an opportunity for a system to track personal items automatically, without having to manually search through bags or perform mental checklists.
One system (described in New Scientist, “Tags to Banish Forgetfulness”, Aug. 14, 2004, p. 19) proposes installing an RFID detector in a wrist watch, and an RFID interrogator in a separate device near a doorway. The RFID interrogator transmits signals to cause RFID tags to transmit their RFIDs. The RFIDs are detected by the RFID detector in the person's watch. If RFID tags are placed on important items carried by the person, then as the person passes the RFID interrogator the RFID detector within the watch will detect any RFIDs which are missing, and notify the person which if any personal items are absent.
This system requires an external and separate interrogator because of the small size of a watches and the size constraints on RFID interrogators. The system is also passive as far as the user is concerned, because the user is only alerted to missing items when passing fixed RFID interrogators placed at strategic locations. And while useful at notifying the user of missing items, the system cannot assist in locating the missing item or indicating where the item was last detected to narrow the range of possible locations when searching for the item.